mutron c200 wah/vol

[adapt]

i've asked for this before, but the stuff is a bit beyond my abilities. it's not a super complex circuit, it's inductorless, and might be the best sounding wah i've ever heard.

schematic here: http://www.freestompboxes.org/download/file.php?id=17298&mode=view

thread here: http://www.freestompboxes.org/viewtopic.php?f=19&t=1353&sid=3ba9431a547ad7e6866d48a459e988c4

[notnews]

It looks like this thread isn't the same as the thread you linked below, so I thought I'd share these... and post them directly in case someone didn't want to go digging for the schems:

Mutron_-_C200_Volume_Wah_(schematic,_modded_for_deeper_filter_like_MutronIII,_by_Boris).JPG

With this effect you can engage the wah and volume circuits simultaneously.. check out the videos demos. Thurston Moore used this a lot.. you can get some seriously awesome sounds with this guy.

Any vero wizards up for the challenge? I took a crack at it but my layout is massive.. I'm not quite at the stage where anyone with a working brain would want to build one of my layouts.

[Alex]

Is the light that goes to LDRs 1,2 & 4 controlled mechanically?
Wouldn't be simpler to control the led brightness with a wah-pot?

[Beaker]

I remember looking inside one of these many years ago. If I recall correctly, the LED is in one of the big black boxes, and the LDRs are in the other, pointing towards each other.. The metal "blade" sits between them and as you rock the treadle plate, the blade moves with it. In this way the blade allows more or less light from the LED to shine on the LDRs.

The LED is fixed brightness, not controlled by a pot, so it just depends on how much light the moving blade obscure/reveals to operate the wah. Again if I'm remembering right, the same LED/LDR/blade arrangement controls the volume too. I do remember though that you can have the wah and the volume operating at the same time.

Quite a neat idea, but mechanically complicated to put into a clone, so I think your idea would be a lot easier Alex.

Here's a photo from the net. It clearly shows the black LED and LDR housings, and the moving blade between them.

[Alex]

I think it would make it easier to fit inside a common wah box.
Now the main question:
LDR 3 is there to regulate the led brightness using the 50K trimpot, correct?
Would you just add a pot between the positive side of the led and V+ or would you eliminate the whole thing and just use a LED, a pot, a fix small value resistor and a trimpot (to regulate the max brightness), all in series?

[Beaker]

"LDR 3 is there to regulate the led brightness using the 50K trimpot, correct?"

That seems to be correct to me.

As to the second part of your question, I really don't know, I think both ways would work, but I have no idea which is best.

[Alex]

Would something like this work?
Apart from the LED's mod, it should match the schematic.
TR1 is to regulate the max LED's brightness.
TR2 is there to help calibrating the Wah Pot (when LED goes off).
Possibly R1=100R, TR1=5K, TR2=50k & 100K Wah Pot?
I don't know if it is theoretically correct but I've breadboarded the LED part and it seems to work.
I've used a regular 100K Log pot to test it.
I don't really build wahs and I didn't have wah pots to test.
You should also test different LED/LDRs combinations.
Here is the possible final version:


If anyone wants to try it, you should first build this one and test the LED/Wah Pot part on a breadboard:


This would make it easier to correct it in case something is wrong or just add the rest later if it works.
Any suggestions or ideas from more knowledgeable people are more than welcome!